The control unit for an electrical generating system, as in an aircraft, requires an accurate measure of current and voltage frequency and phase. In the measurement of frequency and phase of a sine wave, it is necessary to determine the zero crossing of the signal. When the signal is noisy, the zero crossing is masked, the circuit is subject to jitter and the determination of zero crossing is subject to error.
The noise characteristics of a generating system vary for different aircraft models. A zero crossing detector has characteristics which are selected for the aircraft in which the control unit is used. Circuits used in the past have been hard wired of semiconductor components, requiring separate design and construction for different aircraft.
In order to reduce weight, size and part count, control unit circuits have been incorporated in custom chips. This approach is suitable, however, only if the chips can be used with different electrical generating systems so that the design cost may be shared.